针对煤层气井极小半径侧钻增产技术与装备研究中高压水射流钻孔试验的需求，为模拟自进式动态平衡孔底围压射流状态，以更接近实际水射流钻孔试验情况，首先开发了自进式动态平衡围压水射流钻孔试验装置，该装置包含动态平衡测力、动态平衡配重和围压舱三部分，可对直径φ200 mm、长度300 mm的煤样进行淹没状态和10 MPa以内围压下自进力、钻进速度和不同喷头、喷嘴组合的水射流钻进试验。然后利用匀速运动时配重与装置内部密封阻力平衡的方法，对试验装置进行了标定试验，得到了不同围压下，密封件阻力与所需的配重之间的关系式。最后运用此模拟试验装置完成了非淹没、淹没和围压三种状态下水射流钻孔试验，得出了自进式旋转喷头钻进中喷射流量、角度、钻进速度、成孔直径和压力之间的关系。试验结果表明：同等条件下，淹没状态下钻进速度和自进力都有一定减小；围压状态下自进力、钻进速度和成孔直径都随着围压增大而减小，在围压2 MPa后自进力和钻进速度急剧减少；通过对比三种喷头试验结果发现，后喷角度较小时，自进力更大；旋转扭矩较小时，易于卡滞，因此建议选用后喷角为40°的方案，并增大旋转扭矩；同时喷射中实测流量与理论计算流量差别在30%以上，表明喷头有节流现象发生，建议增大喷头过流通径。

Aiming at the requirements of the test on high-pressure water jet drilling in the research of increasing pro- ductivity for the equipment with minimum sidetracking in CBM wells,in order to simulate the status of the self-pro- pelled dynamic balance downhole confining pressure water jet to approach more closely the situation of the actual water jet drilling test,the test device for the self-propelled dynamic balance confining pressure drilling was developed. The device includes three parts:dynamic balance force measurement,counter weight and confining pressure tank. It can conduct water jet drilling test for self-propelled force,drilling rate and different combination of nozzles on coal samples with 200 mm in diameter and 300 mm in length in submerged state and within 10 MPa. Then the calibration test of the test device was carried out by using the method of counter weight and interior sealing resistance balance during uni- form motion,the relationship between the resistance of the sealing element and the required counter weights under dif- ferent confining pressure was found. Finally the water jet drilling test was conducted under non-submerged,submerged and confining pressure status by using the simulating test device,the relationship among the jet flow,angle and drilling rate,hole-forming diameter and pressure of drilling with the self-propelled rotary nozzle was obtained. The test results indicated that under the same conditions and the sub-merged status,the drilling rate and the self-propelled force were reduced at certain extent. Under confining pressure status,the self-propelled force,the drilling rate and the hole-form- ing diameter decreased with the increase of confining pressure,the self-propelled force and the drilling rate decreased sharply after the confining pressure reached 2 MPa. Through the comparison of the test results of three kinds of noz- zles,when the rear injection angle was small,the self-propelled force was bigger,when the rotary torque was smaller,it was easy to be clamped,therefore it was suggested to use the scheme with the rear injection angle 40° and increase the rotary torque. At the same time,the difference between the measured flow and the theoretically calculated flow was more than 30% ,which indicates throttling occurs in the nozzle. It is suggested to increase the nozzle overflow diame- ter.